Exposure apparatuses for semiconductor processing are commonly used to transfer images from a reticle onto a semiconductor wafer during semiconductor processing. A typical exposure apparatus includes an illumination source, a reticle stage assembly that positions a reticle, an optical assembly, a wafer stage assembly that positions a semiconductor wafer, a measurement system, and a control system.
One type of stage assembly includes a coarse stage, a coarse stage mover assembly, a fine stage that retains the wafer or the reticle, and a fine stage mover assembly that moves the fine stage and the wafer or the reticle. More specifically, the control system directs current to the fine stage mover assembly to move the wafer or reticle, and the control system concurrently directs current to the coarse stage mover assembly to move the coarse stage to precisely follow the movement of the fine stage. With this design, the fine stage mover assembly moves the fine stage, and the coarse stage mover assembly moves the coarse stage at the same time and the same rate as the fine stage is moved.
Generally, it is desirable to move the fine stage with as high acceleration as possible to improve system throughput. The coarse stage is typically much heavier than the fine stage. Accordingly, the motor force and heat generated is determined primarily by the acceleration of the coarse stage. Unfortunately, existing high throughput stage assemblies can consume excessive amounts of power and generate excessive amounts of heat.